Positive displacement hydraulic diaphragm type pumps are known in the art for delivery of pumped media, typically fluids, by a pumping action between inlet and outlet valves. Hydraulic diaphragm type pumps make use of a deformable diaphragm fluidly connected to a pumping chamber between the inlet and outlet valves between which the pumped media is moved by constrictive pressure exerted by the diaphragm. The diaphragm is in turn forced to move by a powered mechanical displacement mechanism whose displacement is transmitted to the diaphragm via a working fluid. One particular type of diaphragm is the hose diaphragm.
The deformable hose diaphragm is typically a generally cylindrical membrane, or bladder, with 2 openings, one at substantially each end of the diaphragm, to separate the pumped media in a pumping chamber located inside of the diaphragm from a working fluid surrounding the diaphragm. The hose diaphragm is typically constructed from substantially impervious materials permissive of deformation to change the internal volume of the diaphragm, such as pliable and/or elastic materials like polymeric, plastic, metallic foil, rubber materials, in solid or laminated form, for example. Preferably the pumped media flows from one end through to the other end of the hose diaphragm. Due to the substantially straight flow of the pumped media through the hose diaphragm, and the separation between the pumped media and the working fluid and mechanical components of the pump, this type of positive displacement pump is typically suited for pumping highly viscous materials, abrasive, reactive or corrosive materials, slurries and sludges, as well as less viscous fluids at a wide range of pressures. Although hose diaphragm pumps are discussed in particular below, the field of the present invention applies to all forms of hydraulic diaphragm pumps. In the case of hydraulic diaphragm pumps using an alternate diaphragm other than a hose diaphragm, the description below may be interpreted such that the two working surfaces of the alternate diaphragm correspond to the inside and outside of a hose diaphragm.
Hose diaphragm pumps according to the art may typically provide a constrictive pressure around the hose diaphragm to provide the necessary pumping action of the pumped media inside the diaphragm by displacing a working fluid surrounding the hose diaphragm with a reciprocating piston to constrict (effectively decreasing the internal volume of the hose diaphragm and the pumped media within) and expand (effectively increasing the internal volume of the hose diaphragm and the pumped media within) the hose diaphragm respectively. In the hose diaphragm pumps according to the art, the movement of the reciprocating piston is typically provided by the use of a connecting rod to convert the rotating motion of a drive crank to a reciprocating linear motion to drive the piston. This drive mechanism results in a varying piston velocity over the stroke of the piston due to the arrangement of the crank and connecting rod, wherein the peak velocity of the piston is typically greater than the mean velocity of the piston by a factor of at least 1.6. Although the use of cams have been disclosed in the art to reduce this peak/mean piston velocity factor to some extent, the crank and connecting rod drive mechanism of the hose diaphragm pumps according to the art typically result in a substantial period of acceleration and deceleration of the piston at the ends of the piston stroke, and lag while changing direction. Further, in order to cause a given linear displacement of the piston, it is required to impart a varying degree of rotation of the drive crank, depending upon the location of the piston relative to its stroke limits, thus limiting the precision and accuracy of piston displacement control in the hydraulic diaphragm pumps according to the prior art.
As a result of the characteristics of the crank and connecting rod drive mechanism typically employed in the hydraulic diaphragm pumps according to the art, the pumping characteristics of such conventional diaphragm pumps have several limitations. One limitation is that there is a substantial flow variation during the constriction or expansion phase of the pumping chamber, such that pumped media flows from a pump with even three or more pumping chambers operating in staggered phase are uneven or peaky, typically requiring surge control reservoirs and the like to desirably reduce the peakiness of the pumped media output flow. Another limitation is that the flow variation results in the acceleration and deceleration of both the suction and discharge fluid volumes resulting in dissipation of work to frictional losses. A further limitation is that the peak pressure of the pumped media output flow and the corresponding minimum suction pressure (or peak suction) of the pumped media inlet flow into the pump are significantly higher and lower than the mean pressure and corresponding mean suction, respectively. The minimum suction pressure of the pumped media inlet flow is typically a limiting factor in a diaphragm type pumps due to the requirement to maintain a net positive suction head pressure in the pumped media inlet flow to avoid boiling or cavitation of the pumping media. Yet a further limitation is that in order to produce a given volume of pumped media output flow, the required crank drive input varies depending upon the position of the working fluid piston relative to its stroke.
It is an object of the present invention to provide a positive displacement hydraulic diaphragm pump that addresses some of the limitations of the hydraulic diaphragm pump designs, and particularly hose diaphragm pump designs according to the art.